The purposes of this study are to assess how the body handles baricitinib when it is given with another drug called probenecid. The study doctor will measure the amount of baricitinib that is absorbed into the blood stream and the time that it takes to remove baricitinib from the body. The safety and tolerability of these drugs will be studied. The study will last about 18 days from the first dose to the end of the study (not including screening).